The development of cutting tools for the construction field has always been very active in providing solutions for efficiently and safely cutting reinforced concrete, with a particular focus on providing tools for manually held equipment and to allow the operator to carry out the jobs safely and with minimum fatigue.
Among these tools there is a product called portable diamond chainsaw, which has been developed mostly to perform deep cutting as well as precise square corners cutting with no overcuts. Chainsaws for concrete cutting are in “somewhat” similar to chainsaw for “forestry” wood cutting, the main difference is that the guiding bar features a built-in water feed system and the chain cutters are diamond tipped, usually laser welded to an heavy duty chain chassis. Likewise wood-cutting, most of these tools are hand held and powered with a hydraulic motors or gasoline engines.
While both chain stretches as a result of the unavoidable wear of the chain chassis, the forestry chains are cutting wood and are oil lubricated while the concrete chains are cutting hard concrete, which is often very abrasive and reinforce with steel bars and use water through the guiding bar as only cooling and lubricating means. They are employed with minimal water lubrication and require an average traction power easily double of the ones for forestry. As a result, the chain needs far more frequent re-tensioning cycles, often the cycle takes longer and many re-tensioning device solutions developed for forestry proved to be unsuitable for concrete chainsaws.
Many chainsaws for concrete cutting are powered by hydraulic motors and typically, each re-tensioning cycle requires the user to stop the chainsaw, stop the power-pack oil supply, close water supply to the chainsaw, clean the equipment, take the necessary tools, and operate the chain re-tensioning procedure before resuming operation.
Furthermore, not likewise chains for forestry, chains for concrete cutting are far heavier, subjected to larger centrifugal forces and dynamic loads, and operate in very harsh operating conditions. As a result, they have the tendency to stretch far more rapidly and keeping them properly tensioned within a narrow range during cutting becomes far more critical.
As a matter of fact, the diamond chains life is limited to approximately 8 hours and with frequent chain tension adjustments throughout its cutting life. Each chain tension adjustment requires, essentially, the operator to release the guiding bar and move it outwardly versus the stationary, motorized driving sprocket, thus re-establishing a desired chain tension. This bar displacement is usually provided by means of a suitable chain adjusting device, typically a manually operated screw system.
Once the chain tension tensioning is brought back to normal, it is necessary to firmly re-clamp the bar in a newly established position before resuming operation. It is important to observe that for diamond chains, the correct chain tension does not correspond to a position where the chain is completely tensioned (zero sag) otherwise an intolerable friction would considerably shorten their life. Consequently, during the chain re-tensioning procedure, the operator brings out the guiding bar as much as possible but has then has to retract it back approximately ⅛″ in order to find what it is defined to be the optimal “starting” condition. This, somewhat, aggravates the operator's effort overall. This requirement for retracting the bar back slightly before final re-clamping of the bar makes more difficult any attempt to automate such movement.
The most common system adopted in conventional chain saws to clamp the bar is typically provided by means of two bolts firmly clamping the guidebar sideways against the chainsaw body, while the most common position adjustment means is a screw engaged with the guiding bar which make possible a linear travel of the bar versus the chainsaw body. As a result of these two different means for adjustment, the operator requires a wrench and a screwdriver as basic tools to operate the chain re-tensioning procedure.
This is a well know drawback of the diamond chain sawing system. Due to chassis excessive stretching (elongation), chain re-tensioning becomes inconvenient to the operator due to the frequency of stops and continuous visual monitoring of the tool status in order to run the equipment within a relatively narrow operating range.
Additionally, since the chain tensioning procedure is frequent and inconvenient, operators have the tendency to operate the equipment as much as they can and this becomes a safety hazard for the operator, as a “loose” chain can break and/or create many undesired side effects.
More specifically, usually the bar clamping is provided by two screws which clamp the bar between the cover and the body of the chainsaw. More advanced system use one single bolt eventually locked in position by means of a quick-set lever.
The linear movement of the chain guide-bar away from the chainsaw body and driving sprocket stationary connected thereto, is provided by a screw located inside the chainsaw body operable by means of a screwdriver. More advanced systems, are eventually opting for a cam mechanism or a spiral screw, conveniently integrated inside the chainsaw cover, thus more accessible and quick to be operated.
These known solutions are all fundamentally based on the chainsaw presenting one single body offering no relative movement between the bar clamping system and the motorized chain driving sprocket and they all make possible the take-up of the chain slack by releasing the guiding bar and moving it forward relative to the sprocket.
More precisely, the bar clamping surfaces and bar clamping device allows the bar to slide linearly, relatively to a stationary driving sprocket between two limits, the bar adjust range being typically larger than the predicted overall chain stretch occurring during its operating life, defined by the two limit conditions of new and completely worn out chain.
Basically, portable chainsaws feature a single body, comprising motorized sprocket, bar clamping surface and a cover. The chain tensioning device requires that the bar be unclamped to create a linear movement of the bar moving away from a stationary sprocket in order to compensate for the chain stretch, thus re-establishing a desired chain tension.
The chain operating range for a diamond chainsaw it is typically comprised between one and two inches, thus considerably wider than wood cutting applications. Nevertheless, sometime the chain stretches even longer than the equipment chain tensioning operating range, and the operator has to ultimately remove one or more links from the chain in order to exhaust the chain diamond tips.
FIGS. 1A and 1B show a conventional chainsaw tensioning system for concrete cutting including a chainsaw body 1, a chain guidebar body 12, a guidebar mounting surface 2, bar clamping bolts 3, a tensioning screw 4, a tensioning pin 5, and a water supply slot 6. It also comprises a chain 16, a motorized driving sprocket 8, the primary operator handle 9, the switch level 10, the safety interlock 11, and a secondary operator handle 7. The chain guiding bar 12 features a central slot 13, tension holes 14 and a water inlet 15.
FIG. 1B schematically shows how the operator connects the guiding bar 12 to the chainsaw body 1. In particular, driving sprocket 8 is mounted stationary versus the chainsaw body 1 and is driven by a motor mounted on the back (not visible).
The bar is clamped to the mounting surface 2 by means of clamping bolt 3 in an initial position 14 which is the closest to the driving sprocket 8 and represents the starting point of when chain 16 is new and at its original length. During operation, as a result of chain stretching, the operator is required to perform multiple chain retention cycles. As previously explained, this requires the user to temporarily release bar 12 from the body 1 and, and by means of turning the tension screw 4, relocate the bar in a new position, facing outwardly until chain 16 returns back to normal tension status. After that, bar 12 is firmly re-clamped to the new position by tightening clamping bolts 3. As explained, this is necessary to do a multiple number of times in order to operate correctly and within the desired tensioning range. It is important to observe that diamond chains cannot start operation when the chain is in full tension. As a result, it is necessary to move the bar to a full chain tensioning status and then to retract slightly, making the re-tensioning cycle more complicated.
It is also important to observe, that the bar can be adjusted from two extreme positions indicated in 14 and 15, representing respectively the minimum and maximum bar location within a limited adjust stroke T1, typically around two inches. If the chain stretch exceeds the adjust stroke T1, the operator has no other choice than to shorten the chain (for example, removing a couple of links) in order to exhaust the chain life.
The need for a quick and safe chain re-tensioning system is therefore well known and several attempts have been made to improve it. All known devices are based, though, on easing or partially automating the conventional chain re-tensioning process, which requires unclamping of the guiding bar, moving the guiding bar away from a stationary sprocket by means of a linear motion, and clamping the bar back at a desired new location versus the chain driving sprocket.
Embodiments of the present invention provide a quick chain tensioning system and method, which significantly reduce the operator efforts and time in re-establishing proper chain tension during cutting.